US President Joe Biden said “no” when asked by a reporter at the White House on Tuesday if he was currently discussing joint nuclear exercises with South Korea.

His reply briefly caused confusion as it could be interpreted as contradicting remarks by his South Korean counterpart.

President Yoon Suk-yeol said in an interview with the Chosun Ilbo, published Monday, “The nuclear weapons belong to the United States, but planning, information sharing, exercises and training should be jointly conducted by South Korea and the US. The US has a considerably positive position (on the idea).”

Yoon's top adviser for press affairs, Kim Eun-hye, said that probably Biden had no other choice but to answer “no” because a reporter asked him the question abruptly without context. She added that “joint nuclear exercises can only be held between nuclear weapons states.”

According to Reuters, a senior US administration official said that joint nuclear exercises with Seoul would be “extremely difficult” because South Korea is not a nuclear power, but that the allies are looking at enhanced information sharing, joint contingency planning and an eventual tabletop exercise.

Further explanations by Kim and the US official seem to be made to prevent Biden‘s reply from creating the impression that there are differences between the two allies.

North Korean leader Kim Jong-un recently vowed to increase his country's nuclear weapons arsenal “exponentially” and singled out South Korea as an “undoubted enemy.” He also vowed to develop a new type of intercontinental ballistic missiles that would give the North a “quick counterstrike capability.” Last year it approved a new law authorizing the preemptive use of nuclear weapons.

Considering Pyongyang's escalating nuclear threat, Yoon may have wanted to show through the interview a solid alliance with Washington. However, Biden’s terse “no” effectively weakened any such impression, though that may not have been his intention. But given North Korea's rapid development of ICBMs and nuclear weapons, South Korea and the US have no other choice but to strengthen nuclear deterrence.

North Korea is on the brink of completing intercontinental ballistic missiles that can strike US cities. If it finishes the job, it would be difficult to expect Washington to use nuclear weapons to strike back against a North Korean attack on South Korea. Few US presidents would take the risk of sacrificing a large number of US citizens for the sake of defending South Korea. The US has defended non-nuclear allies through its nuclear umbrella and extended deterrence, but North Korea‘s ceaseless development of ICBM and nuclear weapon programs arouses concerns about the effectiveness of US nuclear umbrella.

South Korea and the international community have striven to denuclearize North Korea but the North has kept on increasing its missile and nuclear capabilities. Denuclearizing the North should remain an objective for Seoul and Washington, but attaining it has become practically impossible. South Korea needs to focus on a more realistic objective, and that is nuclear deterrence.

A sure way to prevent a nuclear attack would be to possess nuclear weapons. In this view, Seoul needs to consider defending itself with its own nuclear weapons. But in reality, it is difficult to put the idea into practice. Seoul has no other choice but to rely on US nuclear weapons to deter a North Korean nuclear attack.

When it comes to fending off North Korea's advancing nuclear and missile threats, as a matter of fact, Seoul and Washington pledged to further strengthen the alliance’s capabilities, information sharing, and consultation process, as well as joint planning and execution. The pledge was contained in the joint communique issued by South Korean National Defense Minister Lee Jong-sup and US Defense Secretary Lloyd Austin following the 54th Security Consultative Meeting held in Washington in November last year.

The US has barred South Korea from accessing nuclear weapons and instead offers its nuclear umbrella. Given the North's nearly complete nuclear missile program, the effectiveness of nuclear deterrence must be raised. If the US puts the pledge into practice early, it will be a significant progress in that direction.